Broadband nulls from a circular array

Circular arrays have the ability to provide a single null in an otherwise omnidirectional pattern. In this paper, a means of characterizing the frequency-dependence of phase modes of a circular array is described. Aspects of phase mode excitation of circular arrays are discussed along with the construction of an experimental four-element null-steering system. Attention is given to the four-element circular array of monopoles used, the Butler Matrix employed to feed the array, a complex attenuator/combiner, phase mode impedance measurements, and pattern measurements. The described study demonstrates a means for the synthesis of instantaneously-broadband nulls.